Pressure indicator



Sept. 16, 1952 Fild OCC. l2, 1946 J. A. STEIN ETAL Sept. 16, 1952 PRESSURE INDICATOR sheets-sheet 2 Filed Oct. l2, 1946 Fig.4.

I INVENToRs Joseg-)h A.Sten 8| John Wagner Syp( TTORFJEY 5 Sheets-Sheet 3 TTORNEY INVENTORS y Joseph A.Sten 8 John W Wagner y J A STEIN ETAL PRESSURE INDICATOR Sept 16, 1952 Filed ce1. 12, 1946 Patented Sept. 16, 195.2

' UNITED STA-rss PATENT; orifice Y v Y Y raussuzloligrcafroi Y I" Joseph A. Stein and John W. Wagner, Pittsburgh,

Pa.,assignors to Bacharach Industrial Instrument Company, Pittsburgh, Pa., a corporation of Pennsylvania 'This invention relates to new' and useful improvements in pressure gages or indicators for measuringk compression and firing pressuresoc.-l curring in thecylinders of diesel engines or the like at any operating speed, and, While not neces sarily so limited, has to do with pressure indi. cators Awhich utilize a precisely calibrated spring as a force balancing the maximum cylinder pressures, the measured deflection of the .spring through suitable indicating means lproviding a reading ofthe compression or firing pressure occurring in the cylinders to which the instrument is attached. y

Indicators of the above character `must func-y tion to indicate the peak pressure of the cyclic varying pressure in thev engine cylinders, and` various means, such as lever devices and'illuminating circuits, for indicating when the peak pressure balances the springpressure of the calibrating device have been heretofore proposed.

Such indicating means are actuated and ener.

gized at the moment the calibratingdevice has been adjusted'to balance the peak pressure of the engine cylinder. The .difficulty with such `prior art devices lies in the inability to detect the slightuctuation-of theleverif mechanical, or in the useof cumbersome electrical and auxiliaryequipment when illuminating circuits are involved. Another diiculty with such prior art is the-tendency to read inaccurately due to the eiiect "of vide va pressure' gage using a piston and cylinder design which', lby' the-provision of a substantial* actuating force at lthe moment the peakl cylinder pressure just overbalances 'therfopposing'f spring pressure,V is insensitive in its 'accuracy'.response to the.v effect: of l carbonaceous` or I tarry l Vdeposits accumulating fromcertain engineL cylinder gases,

requiring only infrequent `cleaning or no cleaning.

atallp v It is another object. of tlieinvention to' provide a pressure f'gage;.fth"e readings of which. are freeV offinertia errorsl i.

'Itisjafurther objectoi the-invention top'rof-v vide apressure gage utilizing-.asingle hand ad- Y ifi claims. (o1. 73-289) justing means forobtaining a positive reading independent of the observer of thepeak cyclically varyingV pressures and forresetting the instru-- ment after such reading is taken. l l

, It is' still anotherobject of theinvention to provide a pressure gage of the above designated character in which changes ,in the calibrated spring can be determined by a direct reading on the instrument to make necessary corrections in the pressure readings obtained. l'

Still a further object of thainvention is the provision of a pressure gage bf the, character herein described which utilizes a piston subject to ya substantial force increment at the pressure balance point that is counteracted by ay calibrated spring and is restricted in its movement to eliminate wear and in response to movement ofwhich portions of the instrument or gage are subjected to accelerated movement to actuate a lockinggor signalling mechanism that determines the position of .the manual adjusting device at which the pressure reading shouldbe taken.

.These and other objects of the invention will become more apparent from a consideration of the accompanying drawings, constituting` apart hereof, in which like reference characters designate like parts, and in which:

Fig. 1 is a side elevationalviewA of'a pressure gage embodying the principles of this invention;

Fig. 2 avertical cross-sectional view thereof including Van adaptor for connectingl the instrument to an engine cylinder; o j` Fig. 3 a cross-sectional view takenl along the line III-III, Fig. 2; l v A Fig. 4 a vertical section, partially in elevation, of a portion of the counter` and reset mechanism;

Figs. 5, 6, and 7 verticalcross-sectional views of the piston and contiguous parts, the locking and the reset mechanism illustrating different positions duringthe operation of the gage;

Figs. 8 and 9 .top plan views,grespectively, of the countershaft and reset mechanism with portions ofthe adjacent parts of the instrument as Will be hereinafter described, and

Fig. 10 is an end view-of the spring the line X-X of Fig. 2.

With referencev to..]5igs.` 1. to 4 and 10of the taken along drawings, the structure therein illustrated com-Y prises a body I having a Wingnut 2 .bywhichf it is'sc'rewed tothe :thread of anA adapteriplug 4 that has a threaded portion 5 .for screwinginto ates. A gas passage 9 is provided in the lower part of the body I to permit engine cylinder gases to exert pressure on the underside of piston 3. The piston movement is limited by a top seat 6a and a pusher rod Ii) bears on the piston 8, the pusher rod being biased by a calibrated double helical spring II. because it deflects such engine cylinder gases as may leak by piston 8 away from other parts of the instrument, 'is mounted for rotary and slid.-L

ing movement on the pusher rod I and-is. provided with serrations or teeth I3. The deiiector plate is provided with a shank I4 having spline'r connections to be rotatable with` a hollow drivev shaft I5 but is freely movable coaxially on the pusher rod. The drive shaft I5 similarly has a spline connection at` I6 with a spring foot I'I and is likewise slidable coaxially relative to the spring foot. The spring foot and drive shaft, as well as the'deflector plate, are. rotatable by a handle I 8 which A rotatesv av spring sleeve. I 9 I that mayj be formed integrally'- with'. ori joined." to the` spring` foot? andL` which'.y interacts ywith. threadsf 28.. of.-vv a barrel 2l, so that-when the handle I8 istrevolved the spring foot is moved axially to shorten or lengthen-the spring. I Ilto2thereby vary the pressure orr'force on pusher rod Ifand consequently against thev piston 8.

A gear wheel`22l ismounted for rotation: with the drive shaft I5- andinteractswith thev teeth of the gear wheel.23 ofi a. counter mechanism mounted inv a` housing. 2 4f; that is'. attached"A toV the' barrel`2 IT. VC'unters'25 are contained within'the. housingf2ll and are-operatedxby a` countershaft' 26;"whichirevolves'withzgearfWheels 22 and 23; A resetdevice 2'1fis1frictionally engaged at'` 28- withv tlrie countershaftto 'be operated thereby,

and ai. light coilspri'ng29w is?. seated on the de-y ilector plate I2! and' abutsagainstthe'shoulder on-tl-ie driveshaftY I 5lto exertonly' suicient .pressure ori-the defleotor. p'latettobias it'normally in a downward direction torestrainplate I 2 :against displacement where thegage is.used;in aposition other than then vertical as shown' in th drawing; 1 f

' 'Atthe top ofn the1.r uslfierP rod.' Iza. sleeve. 3is provided, it being shapedtopass around' the-cross' movement in an' upward direction'f of `the:-'deflec l torplatev I 2-fwouldbringlit'into. engagement with the tip 36lot the Atrigger."33which Wouldrelease lockY 31 fromthelatch 32land spring.'34 ofthe latter .fJould effectl engagementrof the.. dog 38 ofi the latch with the-teeth LI 3 'Iofi thev deflector plate, thus locking it inrpositi'n;

. The arrangementiof" the. trigger, latch,. deflector plate and reset mechanism is more clearly. shown in Figs; 5 to 9 of the' drawings; wherein the reset mechanismfl. isshown outof. engage-V ment with the 1atch'\32' in FigslV and` 6 and in engagement toyreset the .latch and trigger in;Fig; 'l oflthe drawings.

latch and trigger 32:and33 'is shown with refer;- ence-to the deflector plate I2v as a ltop plan view,-

and the functionof the-latch and reset mecha;r

A defiector plate I2, so called` Irl-Fig; 8 the relation ofthev countershaft 2S, reset'mechanism 21. and the' nism will be more fully described in connection with a description of the operation of the entire instrument, which is as follows.

Assuming the adapter 4 to be screwed into the opening of an engine cylinder, as shown in Fig. 2, the handle I8 is turned clockwise to screw down spring foot I1 so as to stretch or lengthen the calibrated spring II and load the piston 8 to a force in excess of the peak, of the cyclic gas pressure force, expected in the engine cylinder. Spring foot Il is then slowly backed off by rotating handle I8 in a counter-clockwise direction to reduce theV spring load on piston 8. Since the counter-clockwise direction of rotation of the handle I8 Will effect a corresponding rotation of drive shaft I5, the gear wheel 23 of the counter mechanism will rotate in a clockwise direction. This direction of rotation moves the reset arm 21 away from the latch 32. The instrument is then ready to take a reading and as slow rotation of thehandlerIS in a counter-clockwise direction is Ycontinued aloading on-the piston'is reached at which the peak cylinder;` pressure forceY justt exceeds the force of spring H onfpiston` 8 and the latter is impelled sharply upward, displacing. pusherl rod Inf upward with'it. Assoon asthev piston 82 moves upward" the slightest' degree off` its-seat ythe; entire-lower area of the piston is'- exposed to the cylinder pressure resulting in a large increase in the force acting on the piston, causing; itr toA move upwardVV Veryrapidly` to its upper seat 6a. Between the time'the-piston 8` leaves its seat 6 and engages its seat 6a tliegases from the engine'pass, bythe piston and-impin'ge against the deiiectory plate I 2, .assisting in speeding/the upward movement of the deiiector plate'. When the pistonv 8 engages its upper seat 6a; itv prevents anyffurth'er passage of the hot engine gases kthr'migh theV indicator and protectsu the indicator-,parts from 'thefdestructive 'action Vof the gases.;t Since the shoulder of the pusher rodnl' engages-thel d'eector plate', I2, the latter will travelxupwardwi'th it and'due Ato the inertia vwill overtravel; thereby; engaging the* tip :i6-'of the'I triggerl 3'3Vwhich-releasesflatch 32.. This'condition isshown vin lEi'g.` iofth'e` drawings. Y

Immediatelyl following. thet piston movement; the cyclically varying pressure in the' engine cylinder-'drops fbelowz the. force of spring I: I f' and the deflector plate I2 and pusher rod: mi' drop down .to thepositionshown in Fig. 5 ofthe draw. ings- Released latch 32A effects engagement of the dog tooth 38 with the-'teeth I3 of the deiie'ctorplate-I'l, and as rotationof the handle I8 is continuedin a counterclockwise direction, the defiector pl'ateIZl tends to pull the latch around` with it,. further rotating. the latchv and exerting.- afdownward Aforce on pist-on 'll-through the pusherrod IUfand deflector plate 'until the piston is 'rmr' 1y locked on its lower seat 6. This locking pre-V vents further .rotation ofV the driveu shaft Ij5, springfoot- |75,- ,spring 'sleeve'` I9' and 1 handle 48; which` indicates to the operator that' the :peak pressure.. been' registered :onf the counter and`A areading is-thenftaken of 'the gasl pressure in thefengineY cylinder at which the pistonmoved. VAfterthe lreading-is taken the` instrument may be.:v preparedr forl another' reading by'fi'rst. re1' ,loadingv1 thet piston by; rotating i handle Ilin,A ai

clockwise direction to increase the force of spring.- I;I;;.1 This; clockwise rotation; of the handlefand. throughxitprotation'of' the drive shaft I15;.re sults in a counter-clockwise rotatiorrofthe 1countershaft 2.6V andlreset arm, 2l.` The'reset arm, whichisfrictionally driven by.- thezcountershaft' 26,1rotates'with .the countersnaft until the end of "the;'reset arm lengages latch '32, as shown in F.rigzs'."y 7, Band 9 of the drawings, rotating the latchv in a clockwise direction and pushing'vthe trigger 3 3 to one side until it is in position 'to catch on the latch.- Reverse vrotation ofV thehan and is kept to a minimum by` careful design'.

However, after prolonged use an instrument spring will show some change in length and for maximum accuracy of readinglcorrectionxfor the changemaybe required. Provisionfis madeto:

check the spring length of' the instrument through the sleeve 30 at the top of the pusher rod I. If handle I8 is turned in a counter-clockwisel direction the spring will first unload and then pull upward in the instrument. Asv the top of the spring moves upward across wire at the top, which is part of the spring II, will engagesnap ring 3I and lift pusher rod I0 up with it. As the pusher rod is raised deflector plate I2 will also be lifted until the .deector plate contacts trigger 33, releasing latch 32, which will engage the teeth I3 of deector plateY I2 and prevent further rotation ofthe handle I8. By noting the reading of the counter 25 when vthe handle locks, a calibration'check gure is obtained which may be used to correct lthe Areading for changes in spring length, or in other words, correct the calibration; or this figure may be'used to reset the counter to give correct read'-v ings. This method of calibration is also employed and the proper counter reading noted on instructions secured to new instruments when tested at the place of manufacture. y e

It is evident from the foregoing description of this invention that the provision of a positive locking device gives a direct positive indication of the time to read the instrument. It will also beobserved Vthat 'in its locked position latch 32 exerts adownward component of force on deflector plate I2, spring plunger I` and piston 8, thus greatly reducing the number of piston strokes perl reading and thereby preventing excessive lower seat destruction.` For this same reason the spacing between ball seat 6 and the upper abutment 6a, permitting piston movement, is very slight. By preventing such destruction4 a narrower, lower seat may be employedy which results in increased instrument accuracy. A narrow seat also results in reduced seat leakage and is selfcleaning. In spite of the small piston travel the provision of a greatly increased piston area on which the engine cylinder pressure acts the in- :stantpiston 8 moves innitesimally off its lower Iseat6 provides a great increase of upward force fat this critical moment causing an upward impulsive thrust on piston 8 which is of such great magnitude momentarily that the spring plunger I0 'carrying' deector plate I2 will be repelled .surlciently to operate the latch and trigger mechanism to lock the handle I8'and the counter device y 'I The over-travel of the deflector plate as provided by inertia and gas pressure requires less tolerances of adjustment and makesy the instrulment less .critical to manufacturing tolerances. L'Thexauton'iatic resetting ofv thelatch mechanism smpn'nesoperauon of the instrument .anaf'p'erf' mits a simple'method of spring checking for maintenance of calibration andaccuracy. 'The provision of a greatlyv increased piston area on which. th'e'engine cylinder pressure acts the `instant piston 8 moves--innitesimally off its lower seat 6 practically eliminates inertia error. Since there would be no inertia error with zero piston movement, it-is obviousthat the inertia errorA appreaches zerov as the piston movement approaches Other structural andV operational advantages` will`v appear obvious to those skilled in the art. Although one form of the device has'been herenillustrated and described, it will be evident. that modifications maybe made in the details of construction without departing from the principles herein set forth. Y "f VWe claim:

1. A pressure gagecomprising a body having' a pressure chamber and a passage adapted for connection to a pressure source, a-piston in said chamber blocking said passage, said chamber having a lower and upper seat for limited movement of said piston; spring means for loading said piston with aiorce opposing the pressure at thepressure source, means for transmittingto said. piston the force developed in said' spring, pres-I sure indicating means, means for varying the force exerted by said spring means, an actuatorI engaging said pressure indicating means with said spring force varying means for loperating said indicating means upon adjustment of the spring force varying means, and means respon-A sive to a predetermined movement of Said piston by the pressure in said pressure chamber for immobilizingv said pressure indicating means whereby the pressure indicating means will posi` tivelyregister the pressure exerted on the piston by the pressure source at the time the piston is moved by said pressure.

2. A pressure gage-comprising a barrel-shaped housing having a pressure chamber with'a gas flow passage' leading at one endto a pressure source, a' piston in said chamber for sealing the pressure source, spaced seats in said chamber for engaging and limiting the degree of move# rnent of said piston and the passage of gas'. through the chamber, a plunger resting'against the piston, a calibrated spring normally biasing said plunger against said piston, means for shortening or lengthening said spring to vary the force exerted on the piston, pressure indicating means mounted Von said barrel having connectionsr with said springvlength varyingy means whereby Vupon movement of rthe latter'said pres-` sure indicatingmeans will be subjected to movement to indicate the vdegree of adjustment of the pressure spring, means for releasably lockingsaid 3.*A pressure gag-e comprisingahousing, a-

barrel sleeve mountedsfor'rotation'on one vend of said housing, a pressure chamber at the other end ofl said housing adapted forY connection' -to a pressure source, -a piston'in saidchamber a plunger resting on said piston, a calibrated spring connected at one end to the plunger and having a spring foot adapted for axial1 movement 'to '1i 8j lenetherrorshertsrr san:`l.v Serine rota on. or oiroctiop tltwaiplvebEesspmcgmeam Where:

n 1 e sentisse-seid Y y i v"r,estolsif/eAe'lelllerit'l V inge theftprssure vactiris'r,"on s aidf press sure respousi-vev el entI at the instant th .so sureirr thenressureeheelber oeo'ses'sli. wr ,te eoentermeonenf to. benseetee L pressure mounteeon .Sais housing.; ne. 7;. In. a pressurev sage iormeasurne tnep'eek oountershaft. and. having; soar tooth. engagement 1o. pressure of a cyclic Vervins pressure inf the clin?.- with said drive shaft, a latch and trigger rlleeh-A dersot engines, a1 pressure roloonilo, lmelt' en ism eneegeablo by Seid. deeotorpleto to look a serine.resistirlsmovmentof .Said pressure. re- Saidnlate. end.. its oonneoted drlve, Shaft en@ sponsi-veelement, for Varying tnepressure barrel Sleeve, against. @if-)hating mOi/61391.15. 31.1.@ a exerted by said springv on rsaid pressurevresponsive Fesf mechanism `Prab1e by rotatong. Ofi the. 1,5 element pressure indicating. means actuated. by; QollnQTShafi t0 reset, Said latch. all@ 12H53@ movementof said spring pressure varying. means mechanism t3o 112162158y the deeior plete, arr-nd. its which vdesignates;the. value of. saidfsprine'pres assoclated rotatmg Parts' sure'for; any pcsitionorsaid pressure varying 4- A Pressure gage compmsmg ai cflrmdrlcal means', meansf operatedby.v movement of. said housing having a' rotatable' SIe-eve ai? gne. end 20 pressure' responsive Velement for locking said thereof, a pressure chamber at the other mth. a. pressure varying andnsai'd pressure'v indicating assage connecting the chamber to a source of s A Y gluid pressure a pressure responsive devicev ,inv mear aga'mstf further movement to thereby reg' er' shaft. for

said passage, a plunger for loading said device to sr th? Vqiuef tik-1.9 ml-balafnmg. massive' if seal said flow passage, a calibrated spring conmg 9.911. 5.9.*1-d`irs-s-u ISPOBSW@ @lmm 11?. neoted at one end to said plunger having a spring msiam?. QI mcvmgm Q? me: latter @me-m' foot connected at its other enCL threaded sleeve l 8" In afpr'eu?? gag-Q. 91; mreawmpg u?? pfazk for-said spring foot being connected to said hous- Qresue. 9E @5l/(.3113. fg-tying: @35,5139 th@ 95.71111? lng sleeve to .be rotated thereby to subject tri@r dere of enemies.. e pressure fesponslre element,

Spring fooi',J to aXal movementto thereby vary 30 a, .Swing @Sistine .Woment of Sadnressure refthe length of the plunger spring, a 'drivep shaft @osi for Vervins. the' 1i .Sr spring on said pressure re.:

Sponsiv element rotated by said spring foot, a deflector plate SHIT@ eiloj. havinga sleeve extending into said drive shaft Snonve Salomon@ v.Cloetlne Ineens`l actuated b and having spline` Connection therewith, spring sonne pressure varylns Ineens' union deel. f biasing said defiector plate in a normal downward rra Ves the 'value'. of said'sprins pressure 'for 'any position, a counter mechanism mounted 0n Sad V 130.5151911 0f Said. @fessure 'Varying mens; means' gage housing having gear wheel connection with IeSllzonSivey 'CQ'InOMCY-ient -Qf Sad TSSU TCS-Dont' said drive shaft, a latch operable in response to sive element for vleck'g' said pressure" Var'ymg movement of Said pressure responsive device to and Ls aid pressure tingfmea against iur; lock said plate, drive shaft, Springl OO' and 40 'ber 'rnoveinent tot ebyfregis't'erthe-valueof housing sleeve against rotary movement in one the'unbalanngpressure'actineupc'aia'g; direction, and a reset mechanism operable Upon sure respoisili/e elernet at'the time ofniov nicht, reversel movement of the housing SloCVQ to reso@ and means for actuatinusavid loolliin'g'rneans'for said latch mechanism and release the. ffectol said pressure'indicatinefmeansf thetension plate.. in said spring 'sfrernov d to'determine-encens' 5, .1p adpressure gage n DITQSSUT Tf?? 4= anyin'th'e legth'of 'sl'ld ,sp ng when unloaded.. sponsive eviceis normay y e asamstasouree s' of fluid pressure by the force 0f a Cainbrated -9 "A gre' 'llglrgmgaifn? palssgae spring and releasedby reducing the Spring fOr-c@ 'pressux'u 'geurigesa pressure re-lbelow the pressure Of the lld, ,Spring fome ad' slporsi-vez'sphe calnerrlbr s'idcharnbe' Vbloclrm justine means, locking mechanism rrlotuated by .I 'rd-bass sdbhalbrhv' wgiw; movement of the pressure responsive device com- Set Qnj'whlc lii'ember hrmam, ts-"spri raisins e @nestor-plate rotatable by movement msftf'itadtnetld 'ineintfiiwttltl'tr-"ai of the spring force adjusting moallS haVDg @Seul Xgsg f th@ i l ce l" teeth to lock saldplate, andatrigger ici holding m??? 0f lite Se g releasingsaidlatoh, the trggerberlgractu waff-d foge-due 't9 the Qressllfe 5.011198 ..Q1 1'.S,21 d ated by movement .of the de ector plete upon @1Q/F39?? .lmlborblng'gyon an .addltlonal movement of the pressure responsive device to. mir-9 tmzemelft fllollgzh exposure of ,a greater release the latch .to thereby lock .the spring force @m03 Qf @lo .llrfftoe thereof Vto the upward adjusting means, .and means for resettingsaid G0 QIC? Whe-1.1119 Vol1- oljoe on said member dueto iatthtmd trigger. presser@ Souroe exeeeds sereeeuesmg spring I6. In a pressure .gage yfor measuring Athe peak mme .aiil'PGSSlro ;1nd1,o.&.ti1;ns. Ineens. .to register pressure .of cyclic .varying pressures in .thecylin- Qffsillepedn .1&1 nlffnberwfhen it receives dersv of yengines a chanber having at one .end S311@ f QIQe Increment. thereof a restricted opening, a pressure respon- 55 .11@ e P-$55,111? lngs oonlim'singn :Dooly helling' on one surface thereof, a latch for .engaging said A 'I1-'rela on vto the' up? sive element conjned within said ,chamber and a zllrel1 .Qhnftbel .2-.Qd of Dnsnee .adapted for adapted normally to seal `with a portion of its @O mooiilol -to .enreSsuresource a presser@ resuriace :said restricted opening, .eine .a variable Snonstvo .member `1n .Seid chamber l.blocking .said

resistance means-acting uponsaidelernent to ,bgtl-v Dlfo, Saidfqhiinl'blxhnving 4a lower and upper. anse said .element .asainstthe .Qusuleoemont eo: 7.o' Sea-t for limiting movement of saidmember, .a tion-*of sarlscylincler pressures-seid 'orrossureror plunger seid-member, .calibrated sponsiye element urrcove ins .saisi restricted ouen.- Sp ns-Qorrnected r.a verle end to saidplunger and me .at the iris-tahoe .of -unbalenoe -tgherebytoex- Connected:.etitsotherendutoa manually adjustpose a greater surface area .to the .engine :presable .Spring rootiorlengthening .and .shortening sure to accelerate :thezmovement thereof .in the 75 -thespring .to varythelorce exertedthereby dn chamber blocking said passage, said chamber having a lower seat on which said member normally rests, spring means for loading said member with a force in excess of the pressure at the pressure source, pressure indicating means, means for adjustment of the spring force in relation to the upward force due to the pressure source on said member, said member being accelerated upward through exposure of a greater portion of the surface thereof to the upward force when the force on said member due to pressure source just exceeds said opposing spring force and means operated by the increased movement of said member to indicate when said pressure indicating mean-s should be read.

12. A pressure gage comprising a body having a pressure chamber and a passage adapted for connection to a pressure source, a piston in said chamber blocking said passage, said chamberVV having a lower and upper seatforrengaging and limiting movement of said piston, a plunger engaging said piston, a calibrated spring connected y atone end to said plunger and connected at its other end to an adjustable spring foot for adjust- 1 ing said spring and varying the force exerted byv said spring upon said plunger, pressure yindicating means, means arranged to be operated bysaid spring foot adjusting means for also adjusting said pressure indicating means, and releasable means for locking said spring footA adjusting means against movement, said piston being so shaped as toprovide a greater area thereof being exposed to the pressure source when it is lifted from its seat to thereby accelerate the operation of said plunger and said releasable loclr-L ing means so that the indicating means will indicate the pressure at the pressure source'towhich movement of the plunger responds.

13. A pressure gage comprising a body having a pressure chamber Yand a passage adapted for connection to a pressure source, a piston in said chamber blocking said passage, said chamber having a lower and upper seat for engaging and restricting movement of said piston, a plunger engaging said piston, a calibrated spring connected at one end to said plungery and connected at its other end to an adjustable spring foot for adjusting the tension in the spring thereby varying the force exerted by said spring upon said plunger, pressure indicating means, means arranged to be operated by said spring foot adjusting means for also adjusting said pressure indicating means, releasable means for locking said spring foot adjusting means against movement, said locking means comprising a deiiector plate movable on the plunger and rotatable with the spring foot adjusting means, a latch and trigger for locking said deilector plate against rotation, thereby locking said spring foot adjusting means,

and a resetting mechanism operable by reverse l movement of the spring foot adjusting means to the calibrated spring that upon reversal of movement of the adjustable spring foot the spring pressed plunger will actuate the latch and trigger to lock the adjusting mechanism and the indicating means whereby any difference in length of the spring as originally calibrated is determinable by the indicating means.

JOSEPH A. STEIN. JOHN W. WAGNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,161,875 Morrow Nov. 30, 1915 1,467,558 Okill Sept. 11, 1923 y 2,046,801 Ulrich July 7, 1936 2,130,649 Okill m Sept- 20, 1938 

